1. Technical Field
The present invention relates to the loading and unloading of flowable cargo transported in lined bulk cargo containers. In particular, it relates to a method and apparatus for using a multiple door bulkhead for installing multiple discharge ports of varying sizes on a standard container liner or on the container liner bulkhead such that a standard container liner can be used for a variety of cargo types.
2. Background Art
Transportation of containers for bulk commodity products (grains, etc) have been implemented using a variety transport vehicles, such as trucks, railroads, and ships. Depending on the nature of the cargo, liners may have to be installed to protect the cargo from contamination (in the case of foods or other perishables) and/or prevent leakage (in the case of powders, small particles, etc.).
An important economic factor in the transportation of bulk commodities is the speed and ease with which the commodities are loaded and unloaded from the container. One factor which effects the speed, and consequently the cost, of loading and unloading containers used for the transport of bulk commodities is the time and expense required to unload the liners due to the type of discharge port used.
The prior art has developed several methods of discharging container liners. One method is the use of narrow tubular discharge ports attached to the rear of the liner. Alternatively, liners have been used which have wide discharge port extending across substantially the width of the liner. This method provides flexibility in terms of preparing a liner for a particular cargo type, but it also has several drawbacks. In particular, the liners are typically made as separate liner types, requiring inventory tracking for each type used. Likewise, it requires additional components, in the form of the bulkheads which are designed for each liner type. The requirement for multiple bulkhead types and liner types increases the total cost of the liners and the bulkheads, thus increasing the cost of discharging the liner.
Typical prior art methods of attaching discharge ports to liners use heat sealing techniques to secure the discharge port to the liner wall. This is usually done at the manufacturing site, and as a result, the user cannot select type discharge port type as needed for a particular cargo type. The inability to select discharge ports for use with a given liner creates another disadvantage for the user. In particular, since many users ship a variety of cargo types, they are then required to store a number of liner types which in turn increases their inventory and storage costs.
In addition to the construction of the liner itself, there is also the issue of the bulkhead type required to support a given liner type. Typical prior art approaches use disposable bulkheads which are designed to work with a liner that has a discharge port in a specific location. Of course, the same drawbacks associated with inventorying and storing multiple liner types applies equally as well to inventorying and storing multiple bulkhead types. Reusable bulkheads, for example those constructed from metal, have the same problem as the disposable bulkheads discussed above. Namely, their structure prevents them from being flexibly used with a variety of liner types, requiring the to be replaced depending on the particular liner used. A shipper who routinely changes cargo liner types will then have to replace the bulkhead and store it for later reuse.
While addressing various aspects of constructing liners and their associated load, vent, and discharge ports, the prior art has typically provided custom solutions which are directed to a particular liner configuration. As a result, users have increased manufacturing costs, increased storage costs, and increased inventory costs. The prior art has not provided a method of constructing a single standard liner and bulkhead system which allows the user to arbitrarily select the discharge port type most suitable for use with a particular cargo type.